A. Field of the Invention
The present invention is directed toward the field of manufacturing integrated circuits.
B. Description of the Related Art
In the manufacture of integrated circuits, diffusion barriers are employed to inhibit the diffusion of metals into regions underlying the diffusion barrier. These underlying regions include transistor gates, capacitor dielectrics, semiconductor substrates, metal lines, and many other structures that appear in integrated circuits. The prevention of metal diffusion is important, because metal diffusion can cause highly resistive pockets to form in regions into which it diffuses. The formation of such resistive pockets can render an integrated circuit defective.
For example, when an electrode is being formed for a transistor's gate, a diffusion barrier is often formed between the gate and a metal that serves as the contact portion of the electrode. The diffusion barrier inhibits the diffusion of the metal into the gate, which may be composed of polysilicon. Diffusion barriers are also employed between the dielectric of a capacitor and the contact portion of the capacitor's electrode. The dielectric may be composed of a material such as tantalum pentoxide, while the electrode's contact portion consists of a metal, such as tungsten, titanium, aluminum or copper. The diffusion barrier prevents the diffusion of the metal into the dielectric. Otherwise, such a diffusion would render the capacitor inoperable.
Refractory metal nitrides have been employed as diffusion barriers. For example, titanium nitride has been employed to inhibit the diffusion of metals, such as copper and aluminum. However, titanium nitride's adhesion to certain surfaces, such as polysilicon and tantalum oxides, is not as high as is desired. Good adhesion is important to provide for the structural integrity of the integrated circuit being manufactured. Good adhesion also provides for better conductivity between the diffusion barrier and an underlying region.
Further, when titanium nitride is deposited on tantalum pentoxide, a reaction occurs. The oxygen from the tantalum pentoxide mixes with the titanium nitride and oxidizes the titanium nitride. This intermixing of the oxygen and the titanium nitride is undesirable, because the presence of oxygen raises the resistivity of the titanium nitride film.
Rapid thermal nitridation has been employed to improve the adhesion of titanium nitride to tantalum pentoxide and reduce the oxidation of titanium nitride. Before the titanium nitride is deposited, rapid thermal nitridation is performed on the tantalum pentoxide substrate to form tantalum oxynitride on the surface of the substrate. The titanium nitride is then deposited on the tantalum oxynitride to which it has better adhesion.
Currently, the rapid thermal nitridation of the tantalum pentoxide substrate and the deposition of titanium nitride cannot be carried out as in-situ operations in the same chamber. As a result, the wafer has to be placed in a rapid thermal nitridation chamber following the deposition of tantalum pentoxide and transferred to a titanium nitride deposition chamber after the rapid thermal nitridation is performed.
It is desirable to minimize the number of different processing chambers that are employed. This limits the number of chamber transfers that must be undergone by a wafer. Chamber transfers are undesirable, because they cause a wafer to be exposed to contaminants in the environment outside of the chamber. Such contaminants can render the wafer defective. Further, the wafer may be exposed to oxygen during transfers. The oxygen can then react with materials on the wafer's surface to increase the resistivity of the wafer's surface material to unacceptable levels.
Accordingly, it is desirable to provide for the formation of a refractory metal nitride film, such as titanium nitride, on a substrate, so that the refractory metal nitride has acceptable diffusion barrier properties and adhesion to the substrate. It is also desirable for any substrate treatment that is performed prior to the deposition of the refractory metal nitride to be carried out in the same chamber as the deposition of the refractory metal nitride.